EARTHING ARRANGEMENTS AND PROTECTIVE CONDUCTORS

Covering: Outcome 2 of Unit 304, Level 3 NVQ Diploma in Installing Electro-Technical Systems and Equipment 2357-13 / 91, or EAL equivalent.

You may find it helpful to have a copy of BS 7671:2018+Amendment 2:2022 for reference to answers.

Q1 TN-C-S, TN-S and TT are all types of?

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Q2 The ‘Earthing Conductor’ is the protective conductor that connects the main earthing terminal (MET), to which other points in both TT and TN systems?

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Q3 Give three examples of suitable earth electrodes that could be installed in a TT installation?

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Q4 What is the minimum cross-sectional area of a buried pvc insulated copper earthing conductor protected against corrosion by a sheath and protected against mechanical damage?

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Q5 The cross-sectional area of a protective conductor, other than a protective bonding conductor, can be determined by one of two methods. What are the two methods?

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Q6 Identify the ‘k’ value to be used in the procedure to select a suitable protective conductor if the protective conductor is the steel wire armour of a 90oC thermoplastic (PVC) SWA cable.

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Q7 A protective conductor is to be selected to be bunched with other cables in a trunking. The protective conductor is to be copper and covered in 700C thermoplastic insulation. If the fault current is likely not to exceed 220A with a disconnection time of 1 second, calculate the minimum size of the protective conductor to be specified.

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Q8 Modern equipment such as switch-mode power supplies, light dimming devices and IT equipment requires a ‘functional earth’ to ensure satisfactory operation. State the requirements for electrical equipment which has a protective conductor current that exceeds 10mA in normal use.

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